In many productions, processing, transportation and storage processes, temperatures, and particularly high temperatures are strictly limited. For example, requirements on the upper limits of temperatures are proposed on the storage and transportation of many drugs in the biomedical field, the storage and transportation of frozen food in the food industry, and constant temperature water bath, constant temperature oil bath and the storage environments of chemical raw materials in the chemical industry. At present, it is not feasible to monitor the temperature of each product in real time in terms of economy and is not completely necessary on practicability. For example, human vaccines are special pharmaceutical products and have strict “cold chain” requirements on transportation and storage, namely each vaccine must be consistently located at a limited low temperature environment in each link of production, storage and issuance, so as to ensure the quality of the vaccine. At present, the incomplete cold chain (for example, vaccines stored in a refrigerator exceed the limited temperature within a certain period of time due to short time power failure) is an important reason resulting in the metamorphism of the human vaccines. The vaccine invalidation resulting from the incomplete cold chain is very difficult to easily identify. The invalid vaccines not only have no epidemic prevention effect on users, but become a kind of injury sometimes, even a fatal threat. Although it is meaningful to monitor the temperature change of each vaccine in real time, from the perspective of economy and technology, the feasibility is very low. The same problem also exists in other industries requiring constant temperature or limited temperature environments, such as frozen food and the like. A simple, reliable, economical and practical method for detecting whether a single product has exceeded the limited maximum temperature and a concrete exceeding value has a very important practical value.
Most of the currently used and reported temperature indication products are based on such technologies as electronic devices, mechanical structures and chemical solutions, etc. Although these technologies are feasible, the application fields are limited, the production processes are complicated and the costs are relatively higher, so that these technologies are very difficult to be applied to the single product.
On the other hand, since more and more traditional anti-counterfeit technologies (for example, laser trademarks, barcodes and patterns and the like) are mastered and copied by the outside world, product counterfeiting has become an increasingly serious social problem. Research and development of new anti-counterfeiting technology have become an urgent need at present.
Many polymer materials have significant shape memory effects, and can sense environment changes and respond to the environment changes in a morphology change (recovering the initial state) manner. At present, thermally driven shape recovery is the most popular driving manner. The principle is to induce the shape recovery via the sensitive properties of the polymers on temperature. Due to the shape memory effects and the low costs, the polymers become a relatively ideal selection of manufacturing cheap temperature indication products in large scales. On the other hand, we can indicate the authenticity of a target article according to the rule of the polymers of gradual morphology change with temperature rise in the shape recovery process.
Patent documents 201210206952.X, 201210480325.5 and 201210512085.2 respectively disclose a temperature indication label and method for temperature indication via a shape memory effect of a shape memory polymer and a multilevel anti-counterfeit indication label and method for anti-counterfeit indication. The basic method is to form multiple predeformations with different recovery temperatures at different temperatures above the initial glass transition temperature or melting transition temperature of the shape memory polymer, so as to form the temperature indication label and method capable of indicating the environment temperature and the multilevel anti-counterfeit indication label and method. Although these products and methods achieve the temperature indication and anti-counterfeit effects, when manufacturing the labels, the multiple predeformation treatments still need to be completed at different temperatures, and the steps are very complicated, which is not conducive to improving the manufacturing efficiency and lowering the cost.
The existing experiments have proved that, for the shape memory polymer, after the predeformation is formed at a certain temperature, the recovery degree of the predeformation is relevant to the predeformation size and the specific heated temperature. In simple terms, specifically, for multiple predeformations with different deformation amounts of a specific shape memory polymer formed at the same temperature, the shape recovery temperature necessary for the predeformation with a smaller deformation amount is lower, while the shape recovery temperature necessary for the predeformation with a larger deformation amount is higher. How to utilize this property of the shape memory polymer to perform temperature indication or multilevel anti-counterfeit indication is involved in no technology currently.